    // 导⼊必要的Java Swing和AWT库
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
    // ShapeDrawerGUI类继承⾃JFrame，⽤于创建图形⽤户界⾯
    public class ShapeDrawer extends JFrame {
        // 定义⼀个DrawArea对象，⽤作绘图的主要区域
        private DrawArea drawArea = new DrawArea();
        // ShapeDrawerGUI的构造函数
        public ShapeDrawer()   {
            this.setSize(400, 400); // 设置窗⼝的初始⼤⼩
            // 设置默认关闭操作，退出程序
            this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            this.setTitle("图形绘制器"); // 设置窗⼝标题
            // 将绘图区域添加到窗⼝的中央
            this.add(drawArea, BorderLayout.CENTER);
            // 创建⼀个下拉列表（JComboBox），⽤于选择要绘制的图形类型
            JComboBox<String> shapeSelector = new JComboBox<>(new String[]
                    {"正⽅形", "⻓⽅形", "圆形", "三⻆形"});
            // 将下拉列表添加到窗⼝的北部（上⽅）
            this.add(shapeSelector, BorderLayout.NORTH);
            // 为下拉列表添加事件监听器，以便在⽤户选择不同选项时做出响应
            shapeSelector.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    JComboBox cb = (JComboBox) e.getSource();
                    String shapeName = (String) cb.getSelectedItem();
                    int size = 0; // 初始化尺⼨变量
                    boolean validInput = false; // 标记⽤户输⼊是否有效
                    while (!validInput) { // 循环直到⽤户输⼊有效
                        String input = JOptionPane.showInputDialog("请输⼊" + shapeName
                                + "的尺⼨:");
                        try {
                            size = Integer.parseInt(input); // 尝试将输⼊转换为整数
                            validInput = true; // 如果成功转换，标记输⼊有效并退出循环
                        } catch (NumberFormatException ex) {
                            JOptionPane.showMessageDialog(null, "输⼊⽆效，请输⼊⼀个整数。"); // 如果失败，提示⽤户重新输⼊
                        }
                    }
                    drawArea.setShape(shapeName, size); // 更新图形和尺⼨
                }
            });
        }
        // 主⽅法，程序的⼊⼝点
        public static void main(String[] args) {
            // 使⽤SwingUtilities.invokeLater
            // 来确保GUI的创建和更新在事件派发线程上执⾏
            SwingUtilities.invokeLater(new Runnable() {
                @Override
                public void run() {
                    // 创建ShapeDrawer对象，并使窗⼝可⻅
                    new ShapeDrawer().setVisible(true);
}
        });
    }
    // DrawArea类继承⾃JPanel，⽤于⾃定义绘图逻辑
    private static class DrawArea extends JPanel {
        // 默认绘制的图形是正⽅形
        private String shape = "正⽅形";
        private int size = 100; // 添加尺⼨属性，默认为100

        // setShape⽅法⽤于更新当前要绘制的图形
        public void setShape(String shape, int size) {
            this.shape = shape;
            this.size = this.size;
            this.repaint(); // 调⽤repaint⽅法来重绘⾯板
        }
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            switch (shape) {
                case "正⽅形":
                    g.drawRect(50, 50, size, size);
                    break;
                case "⻓⽅形":
                    g.drawRect(50, 50, size * 2, size);
                    break;
                case "圆形":
                    g.drawOval(50, 50, size, size);
                    break;
                case "三⻆形":
                    int[] xPoints = {50 + size / 2, 50, 50 + size};
                    int[] yPoints = {50, 50 + size, 50 + size};
                    g.drawPolygon(xPoints, yPoints, 3);
                    break;
            }
            }
        }
    }

